1. Technical Field
The present invention relates to axial fans (given simply to be “motors” hereinafter), in particular to axial-fan motor structures involving 10,000 rpm and faster high-speed rotation.
2. Description of the Related Art
Owing to improvements in the processing speed of integrated circuits employed in server computers, the amount of heat emission from servers themselves has been on the rise in recent years. Thus, securing the airflow volume necessary in order stably to cool server-computer integrated circuits has become a critical requirement demanded of server-cooling fan motors. Consequently, there has been an urgently felt need to improve the revs of fan motors.
Nevertheless, improving the motor revs entails the problem of heat emission from the motor itself increasing. That is, the goal of raising the revs in a motor gives rise to the necessity of passing greater current to the motor's stator, and this turns out to cause the stator to emit heat. In conventional motor structures, because the positional relationship between the motor stator and bearing unit is one in which they are radially opposed across a bearing retainer, heat from the stator gets transmitted to the bearing unit via the bearing retainer. On that account, the bearing unit is subjected, more than is necessary, to the influences of the heat produced by the stator, which has led to the problem of the bearing lifespan consequently being shortened. Moreover, the bearing unit is continually subjected to strong rotational impact due to the increase in motor revs. The rotational impact causes the bearing(s) itself to emit heat, shortening the bearing lifespan all the more.
In that raising the motor revs also makes the motor's magnetic-pole switching more frequent, the vibrations produced when the magnetic poles are switching turn out be a serious problem.